HMF Honda TRX 450R 2007 - 2014 Black Slip On Exhaust Muffler & Jet Kit The Performance Series uses a 2 1/8" non-restrictive core for maximum flow. Depending on the model, you can expect a 4-6 dB increase over stock. The exhaust shell is made of T6061 Aluminum that weighs substantially less than stock. USFS Approved: All HMF offroad exhausts come with a USFS approved spark arrester. Included: Individual Keihin Hex Jets: 135, 160, 165, 170, 48 Pilot